The present invention relates to rotary regenerative air preheaters which employ a rotor post for rotation of the rotor and more particularly to novel rotor post headers for mounting the rotor diaphragms.
A rotary regenerative air preheater transfers sensible heat from the flue gas leaving a boiler to the entering combustion air through regenerative heat transfer surface in a rotor which turns continuously through the gas and air streams. The rotor, which is packed with the heat transfer surface, has a rotor post which is supported through a lower bearing at the lower end of the air preheater and guided through a bearing assembly located at the top end for most vertical flow air preheaters. Some vertical flow air preheaters use a top support bearing and a lower guide bearing. The rotor is divided into compartments by a number of radially extending plates referred to as diaphragms. Generally, the bottom inboard edge of the diaphragms are set on a ledge on the lower rotor post header and an upper diaphragm tongue is pinned within an annulus in the upper rotor post header.
In a typical rotary regenerative heat exchanger, the hot flue gas and the combustion air enter the rotor shell from opposite ends and pass in opposite directions over the heat exchange material housed within the rotor. Consequently, the cold air inlet and the cooled gas outlet are at one end of the heat exchanger, referred to as the cold end, and the hot gas inlet and the heated air outlet are at the opposite end of the heat exchanger, referred to as the hot end. As a result, an axial temperature gradient exists from the hot end of the rotor to the sold end of the rotor. In response to this temperature gradient, the rotor tends to distort and to assume a shape similar to that of an inverted dish (commonly referred to as rotor turndown). This distortion causes the diaphragm tongues to move up their mounting pins, imposing a tensile stress on the diaphragm tongue, the pin and the flanges on the upper rotor post header that define the annulus. Consequently, the upper rotor post header comprises a massive structure to provide an annulus having a sufficient height to allow movement of the diaphragm tongue and flanges having sufficient thickness to withstand the tensile stress imposed by the rotor distortion. Such a structure is expensive to manufacture and imposes a large weight burden on the rotor bearing.